David Blunkett has taken a job advising a company interested in bidding to run Britain's controversial identity cards programme, a policy he was the architect of and championed in government.

The former Home Secretary took up the post for the Texas-based security firm Entrust, which specialises in securing digital information and combating identity theft, earlier this month. The firm already provides software for the Spanish national ID card system and has formally registered an interest in the British project.

Blunkett is bound by a two-year ban on lobbying British ministers and officials from the date he resigned as Work and Pensions Secretary in November 2005. That does not expire until this November. His spokeswoman insisted yesterday that he would not be working in Britain for the company and would only advise on overseas work.

However, David Davis, the shadow Home secretary, last night attacked the decision, saying: 'David Blunkett was a staunch champion of ID cards and involved right at the heart of the project. The British public will be rightly sceptical about his involvement with a company that could benefit lucratively from this £20bn scheme.

'Under no circumstances should IT companies receive any preferential treatment and ex-ministers should not use their contacts to obtain any special treatment. Mr Blunkett should make sure he abides by this.' The Tories have pledged to scrap plans for ID cards, which they describe as a 'plastic poll tax', if they get into power.

Blunkett was one of the government's biggest defenders of identity cards when at the Home Office, before resigning over his involvement in a visa obtained for his lover's nanny. He maintained his interest in the scheme when he re-entered the cabinet as Work and Pensions Secretary: ID cards are potentially useful in the fight against benefit fraud.

He has described ID cards as 'not a luxury or a whim - it is a necessity'. Two weeks before he started the job, he wrote in his column for the Sun that ID cards would 'protect our identity from fraudsters, stop illegal foreigners in their tracks, save billions being leeched from our welfare system and beat organised crime'.

ID cards will become compulsory for new British passport-holders from 2010. Making them compulsory for all Britons, including those who do not have or choose not to have passports, would require further legislation but the government has made it clear that it expects the majority of the population to get identity cards as they replace expiring passports.

Phil Booth, of the campaign group No2ID, which was set up to fight the introduction of the cards, said that having helped draw up the initial legislation Blunkett was extremely well informed about the process and had also been closely involved in negotiations across Europe about identity and security, knowledge of which could be of interest to a US company. Entrust has offices in nine European countries including Britain. He said. 'Maybe Mr Blunkett has a keener or more recent experience of what clearly is quite a Byzantine legislative field.'

Entrust has formally registered an interest in the British ID cards project, via a scheme for potential future suppliers to notify themselves to the Home Office's Identity and Passport Service, and has attended two seminars organised for the ID cards programme.

The post as chair of Entrust's international advisory committee is declared in Blunkett's latest entry for the Commons register of members' interests. A spokeswoman for the Advisory Committee on Business Appointments said it had also been notified and that it approved, subject to the two-year moratorium on lobbying in Britain.

The spokeswoman for Blunkett said: 'He is not involved in the UK side. His contract excludes him doing work in the UK. It is about advice for overseas work. Obviously he has taken advice from the advisory committee and he's absolutely going to adhere to the advice.'